JPH09185255A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which prevents the occurrence of ghost in any conditions and ensures satisfactory image formation. SOLUTION: Because the surface of a developing roller 56 and the surface of a photoreceptive drum 20 are rotating in opposite directions to each other in the position where they are the nearest to each other (nip part), the formation of a toner image from an electrostatic latent image and the attraction and recovery of residual toner are separately carried out before and after the nip part, and improvement in the capability of attracting and recovering the residual toner is possible. Also, the developing roller 56 is made of an conductive elastic body and the peripheral speed of the developing roller 56 is two or more times that of the photoreceptive drum 20, therefore by the residual-toner scrape effect of the developing roller 56 the capability of attracting and recovering the residual toner can be further enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer, a facsimile or a copying machine, and in particular, a so-called cleanerless system in which residual toner after transfer is used for developing again without being stored as waste toner. And an image forming apparatus using the same.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a laser printer or a copying machine, the residual toner remaining on the photoconductor after transfer is scraped off by an elastic blade and stored in a dedicated waste toner case. It had to be stored and periodically disposed of.

However, in such an image forming apparatus, toner is scattered due to soiling of hands and clothes when the toner is discarded, and damage of the discarded toner case during transportation of the discarded toner case. However, it is not desirable from an ecological point of view.

Therefore, a so-called cleanerless method has been proposed in which the residual toner on the photoconductor is collected by the developing means and used again for the development.

FIG. 9 shows an example of an image forming apparatus using a cleanerless system.

In the laser printer 200 shown in FIG. 9, generally, at the bottom of the main body case 202, a paper feed cassette 214 and a paper feed for feeding the papers P contained in the paper feed cassette 214 one by one. A roller 213 is provided, and a photoconductor drum 220 is provided on the upper side of the roller 213, and a transfer roller 260 that comes into pressure contact with the photoconductor drum 220 from below.
Is provided, a fixing unit 270 is provided close to the photoconductor drum 220, and a paper discharge tray 277 is provided above the photoconductor drum 220. That is,
A transport path P for the paper P fed from the paper feed cassette 214
As shown by the alternate long and short dash line, the P is formed in a zigzag shape that is folded back a plurality of times, so that the laser printer 200 can be downsized.

Then, after the charge on the photoconductor drum 220 is wiped off by the charge elimination lamp 241, the surface of the photoconductor drum 220 is uniformly charged to a predetermined polarity by the charger 240, and then the laser scanner unit 230 is operated. The emitted laser light L is irradiated onto the photoconductor drum 220 to form an electrostatic latent image. The electrostatic latent image is integrally provided in the toner cartridge 250 and is in contact with the photoconductor drum 220. The charged toner received from the developing roller 256 is developed into a visible image to form a toner image. Then, the toner image is transferred onto the conveyed paper P by the transfer roller 260, and the toner image on the paper P is further transferred to the paper P by the heating roller 271 of the fixing unit 270.
The image-formed sheet P is finally discharged onto a sheet discharge tray 277. On the other hand, the residual toner remaining on the photosensitive drum 220 after the transfer is temporarily stored in the cleaning roller 280 by applying a voltage having a polarity opposite to that of the toner to the cleaning roller 280.
Then, after the transfer process to the paper P is completed, the transfer residual toner accumulated on the cleaning roller 280 is discharged onto the photosensitive drum 220 again by applying the voltage of the same polarity as the toner to the cleaning roller 280 this time. Then, the developing roller 256 causes the toner cartridge 25 to
Collected to 0.

Here, in the toner cartridge 250, the developing roller 256 and the supply roller 25 that presses and contacts the developing roller 256 to supply the toner 253 to the developing roller 256.
5 is rotatably provided, and the developing roller 25
6 is provided with a layer thickness regulating blade 257 that regulates the layer thickness of the toner 253 adhering to 6 to a predetermined thickness and charges the toner 253. The excess toner 253 removed by the layer thickness regulating blade 257 is supplied to the supply roller 255. The developing roller 256 and the supply roller 255 are driven in the rotational direction as shown so as to drop upward.
That is, the developing roller 256 develops the toner 253 while charging the toner 253 with static electricity having a predetermined polarity.
It is configured to be driven while being pressed and contacting in a rotation direction different from the rotation direction of 20. That is, the developing roller 256
In the nip portion of the photosensitive drum 220 and the photosensitive drum 220, both are driven so as to move in the same direction.

By the way, the laser printer 20 shown in FIG.
In No. 0, the toner 253 used is a polymerized toner having excellent fluidity. If the pulverized toner is used instead of the polymerized toner, the fluidity is poor, and the amount of residual toner remaining on the photosensitive drum 220 after transfer is increased. Further, the cleaning roller 280 and the developing roller 2
The ability of 56 to collect the residual toner is also reduced, and as a result, the residual toner is not sufficiently recovered and reaches the transfer area again, and is transferred to the paper P by the transfer roller 260. Then, the photosensitive drum 22 is placed on the paper P.
An afterimage (hereinafter referred to as a ghost) is generated by the residual toner remaining at 0.

[0010]

By the way, generally, the polymerized toner and the pulverized toner each have advantages and disadvantages,
Which one is better cannot be said unequivocally.

The pulverized toner is prepared by kneading wax, CCA (charge control agent) and colorant (carbon black is generally used in the case of black) into a resin such as styrene acrylic or polyester and then pulverizing the mixture. To do. Since it is crushed and produced, its shape is irregular and has many corners, and its fluidity is poor. As a result, the spread in the developing device is poor and the transfer efficiency is low, but since the leakage of toner from the minute gaps is reduced due to the poor fluidity, the design of the sealing material to prevent toner leakage is It's easy.

[0012] On the other hand, the polymerized toner, although its component is not much different from the pulverized toner, is completely different in its manufacturing method. Since the polymerized toner is produced by dispersing the material in a solvent, its shape is almost spherical due to the influence of surface tension. With the current technology, it is difficult to produce a polyester toner by a polymerization method, and a styrene acrylic resin is mostly used. Since this polymerized toner has a perfect spherical shape, it has very good fluidity, and as a result, it spreads well in the developing device and the transfer efficiency is high. The amount of toner leaking from the toner increases, and it is difficult to design a sealing material for preventing toner leakage.

The laser printer 200 shown here is also used.
Then, as shown by the alternate long and short dash line in FIG.
Since P is bent, there is no need to use special paper such as thick paper or envelope which is unfavorable for transfer as the paper P, but if this conveyance path is made straight, there is an opportunity to print on thick paper or envelope. In that case, the amount of residual toner remaining on the photoconductor drum 220 without being transferred increases, and the ghost is generated on the paper P in the same manner as described above, exceeding the recovery capability of the cleaning roller 280 and the developing roller 256. become.

That is, as described above, in the cleanerless type image forming apparatus, it is difficult to use the pulverized toner which is easy to produce but has low transfer efficiency. Therefore, it is difficult to produce a polymerized toner which is excellent in transferability but difficult to produce. Should be used,
Therefore, there is a problem in that it is very difficult to design a sealing material for preventing toner leakage that tends to occur around the developing roller 256.

Even when the polymerized toner is used, when an image is formed on special paper such as thick paper or envelope having poor transferability, the residual toner remaining on the photosensitive drum after the transfer, especially in a low temperature and low humidity environment. However, there is a problem in that the ghost is generated due to the increase in the number of particles, which cannot be completely collected by the developing roller.

Although generally referred to as cleanerless, in practice, means for temporarily storing residual toner during printing, as represented by the cleaning roller 280 shown in the above-mentioned conventional example. However, there is also a problem that one extra power source is required as compared with the system using a cleaning blade for scraping off the residual toner.

If a toner leveling brush for equalizing the distribution of the residual toner on the photosensitive drum is used instead of the cleaning roller, the above power supply is not required, but this means still produces residual toner. There was a problem that ghosts could not be dealt with when the number increased.

The present invention has been made to solve the above-mentioned problems, and in an image forming apparatus called a cleanerless system, pulverized toner is used, an image is formed on thick paper or an envelope, and low temperature and low humidity and high temperature are used. An object of the present invention is to provide an image forming apparatus capable of forming an excellent image without causing a ghost even when used in a condition where the amount of residual toner tends to increase such as image formation in a high humidity environment.

[0019]

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention forms a latent image forming means for forming a latent image on the surface of a latent image holding member and the latent image forming means. And a developing unit for bringing the toner thin layer formed on the surface of the toner carrier into contact with the surface of the latent image carrier, and developing the latent image into a toner image; and an image transfer unit for transferring the toner image to the surface of the image carrier. The developing means converts the latent image into a toner image,
An image forming apparatus for collecting, by the toner carrier, residual toner remaining on the surface of the latent image carrier after the transfer, wherein the latent image carrier is driven in a predetermined direction in synchronization with conveyance of the image carrier. The first drive means and the surface of the toner carrier at the position closest to the surface of the latent image carrier,
Second drive means for driving in a direction relatively opposite to the moving direction of the latent image carrier surface is provided.

The operation will be described. The latent image is formed into a toner image by bringing the thin toner layer on the surface of the toner carrier of the developing unit into contact with the surface of the latent image carrier on which the latent image is formed by the latent image forming unit. This toner image is transferred onto the image support surface by the image transfer means. On the other hand, the residual toner remaining on the surface of the latent image holding member without being transferred is collected by the toner carrier. The surface of the latent image carrier is driven in a predetermined direction in synchronization with the conveyance of the image carrier by the first driving means. The surface of the toner carrier is driven in a direction relatively opposite to the moving direction of the latent image carrier surface at the position closest to the surface of the toner carrier by the second driving means. The latent image carrier surface and the toner carrier surface are driven in relatively opposite directions at the closest position, so that the latent image is formed into a toner image by the upstream side in the moving direction of the toner carrier surface from the closest position of both. Since the residual toner is collected on the downstream side in the moving direction of the surface of the toner carrier from the closest position of both, the toner image formation and the collection are performed separately, and the residual toner is collected on the toner carrier. It is possible to improve the recovery ability of the.

An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the toner carrier is an elastic roller having conductivity.

Explaining the operation, the same operation as in claim 1 is achieved, but by using a conductive elastic roller for the toner carrier, it becomes possible to increase the friction coefficient on the surface of the toner carrier, and As a result, the toner conveying force becomes stronger, so that the ability to collect the residual toner can be further enhanced.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the moving speed of the surface of the toner carrier by the second driving means is changed to the latent image by the first driving means. The moving speed of the surface of the holder is twice or more.

Explaining the operation, the same operation as in claim 1 or claim 2 is achieved, but the moving speed of the surface of the toner carrier is made twice or more as high as the moving speed of the surface of the latent image carrier. As a result, the effect of scraping off the residual toner by the surface of the toner carrier is increased, and the residual toner recovery capability can be further enhanced.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, the present invention is applied to a laser printer equipped with a feeder unit, a photosensitive drum, a laser scanner unit and the like.

As shown in FIG. 1, this laser printer 1
Inside the main body case 2, a feeder unit 10 for feeding a sheet of paper (corresponding to an image support) P for image formation, and a photosensitive drum (corresponding to a latent image holder) 20 for receiving a laser beam L are provided. And a charging unit 40 for charging the photosensitive drum 20 to a predetermined potential, and a laser scanner unit for forming an electrostatic latent image on the charged photosensitive drum 20 (latent image formation by the charging unit and the laser scanner unit. 30) and a developing roller (corresponding to a toner carrier) 5
6, a developing unit 50, a transfer roller (corresponding to an image transfer unit) 60 that transfers the toner image on the photosensitive drum 20 onto the paper P, a fixing unit 70, and a paper discharge that discharges the paper on which the image is formed. Tray 77 and photosensitive drum 2
A first drive mechanism 80 that drives 0 and a second drive mechanism 100 that drives the developing roller 56 and the like are provided.

First, the feeder unit 10 will be described.

As shown in FIG. 1, a paper pressing plate 11 having a width dimension substantially the same as that of the paper P is arranged in the feeder case 3 above the rear end of the main body case 2 and presses the paper. The plate 11 is pivotally supported at a rear end thereof and elastically biased upward by a compression spring 12 at a front end thereof, and a paper feed roller 13 extending in the left-right direction is rotatably supported. The paper feed roller 13 is rotationally driven at a paper feed timing by a drive system (not shown).

Then, the paper P is accommodated in the feeder case 3 in an inclined shape, and the upper paper P is fed one by one by the rotation of the paper feed roller 13. Further, in order to prevent two sheets of paper P from being inserted, the separating member 15 provided below the paper feed roller 13 is elastically biased to the paper feed roller 13 by the compression spring 16. Here, the paper feed roller 1
Transport direction from 3 (from rear to front in FIG. 1)
On the downstream side, a pair of registration rollers 17 and 18 that align the leading ends of the fed paper P are rotatably supported.

The photoconductor drum 20 is shown in FIG. 1, FIG. 2 and FIG.
As shown in FIG. 5, a photoconductive layer 22 of a predetermined thickness (for example, about 20 μm) made of a photoconductive resin based on polycarbonate is provided on the outer peripheral portion of a cylindrical sleeve 21 made of aluminum.
Is formed, and is rotatably supported by the main body case 2 with the cylindrical sleeve 21 grounded. That is, the toner 53 charged in the positive polarity is added to the electrostatic latent image of the positive polarity formed on the photosensitive drum 20.
Is developed by a reversal development method.

The laser scanner unit 30 is disposed below the photoconductor drum 20, and a laser light emitter 31 for generating a laser beam L for forming an electrostatic latent image on the photoconductor drum 20 is rotationally driven. Polygon mirror (for example, 5
A surface mirror) 32, a pair of lenses 33 and 34, a pair of reflection mirrors 35 and 36, and the like. An electrostatic latent image can be formed on the photosensitive drum 20 with the laser light L emitted from the laser scanner unit 30.

On the other hand, a scorotron type charger for generating a corona discharge from a charging wire made of tungsten or the like at a position on the advance side in the rotation direction with respect to the position on the photosensitive drum 20 where the laser beam L is irradiated. 40 is provided, a charge eliminating lamp 41 is provided at a position further advanced in the rotation direction than the charger 40, and transfer residual toner on the photosensitive drum 20 is provided at a position further advanced in the rotation direction. A toner leveling brush 42 is provided so that the brush tip contacts the photosensitive drum 20.

Next, the developing unit 50 arranged immediately behind the photosensitive drum 20 will be described.

The developing unit case 4 has an agitator 52 that is driven to rotate and an insulating toner 53 that has electrical insulation.
A double-cylindrical toner box 51 accommodating and is attached detachably, and is supplied to the front side of the toner box 51 by rotation of an agitator 52 via a toner supply port 51 a formed in the toner box 51. Toner 53
A toner storage chamber 54 for storing the toner is formed in the toner storage chamber 54, and a supply roller 55 is horizontally arranged in the left-right direction and rotatably supported. Further, the supply roller 55 is provided so as to partition the front side of the toner storage chamber 54.
The developing roller 56 is horizontally arranged in the left-right direction so as to be in contact with the photosensitive drum 20 and is rotatably supported.

Here, the toner 53 is a polymerized toner made of styrene-acryl or the like which is closer to a spherical shape than the pulverized toner, and its particle size is about 7 to 10 μm.

The supply roller 55 is a conductive elastic foam made of silicon rubber, urethane rubber, or the like.
The resistance value at the contact portion with the developing roller 56 is about 5 × 1.
It is set to 0 ⁴ to 1 × 10 ⁹ Ω.

The developing roller 56 is a conductive rigid roller made of silicone rubber, urethane rubber, NBR, or the like, and has a resistance value from the central electrode to which a developing bias voltage is applied to the outer peripheral contact portion. , About 5 × 10 ⁴
It is set to ~ 1 x 10 ⁷ Ω.

Here, in the toner storage chamber 54, a large upper space S above the supply roller 55 is provided, and as shown in FIG. 2, the toner 53 of the toner box 51 is replaced by the toner supply port 51a. Even when a large amount is supplied to the toner storage chamber 54 via the toner 53, the toner 53 is not packed and solidified. Therefore, the toner 53 is always in the form of powder and its fluidity is always maintained, and the supply roller 55
As a result, it is possible to stabilize the toner supply.

On the other hand, a thin plate-like elastic layer thickness regulating blade 57 made of stainless steel or phosphor bronze is attached to the developing section case 4 downward, and the bent portion formed at the lower end portion thereof is the developing roller 56. The layer thickness of the toner 53 supplied from the supply roller 55 and adhered to the surface of the developing roller 56 in a layered manner by the layer thickness regulating blade 57 is a predetermined thickness of about 1 layer (about 7 to 12 μm)
Regulated by. That is, the amount of toner on the developing roller 56 is
The radius of curvature of the bent portion is about 0.3 mm so as to be set to about 0.5 mg / cm ² . As a result, since the toner 53 on the developing roller 56 after the layer thickness is regulated is one layer strong, the toner 53 that has not been subjected to the development does not accumulate on the contact portion with the photoconductor drum 20. The toner is surely attached to the developing roller 56 and collected.

The photosensitive drum 20 and the like are rotationally driven clockwise in a side view by a first driving mechanism 80 described later, and the supply roller 55 and the developing roller 56 are driven by a second driving mechanism 100 described later. ., The toner particles 53a of the toner 53 are rubbed by the supply roller 55 and the developing roller 56, as shown in FIG.
The toner 53, which is positively charged by the pressure friction of the developing roller 56 against the developing roller 56, adheres to the electrostatic latent image formed on the photosensitive drum 20 by the laser light L and is inverted. It is developed by the development method.

Next, the transfer roller 60 is connected to the photosensitive drum 2
0 is a foam elastic body having conductivity, which is provided so as to be in contact with the upper side of 0, is rotatably supported, and is made of silicon rubber, urethane rubber, EPDM, or the like.
The resistance value at the contact part with is about 1 × 10 ⁶ to 1 × 10
It is set to ¹⁰ Ω. When transferring the toner 53 on the photosensitive drum 20 to the paper P, the transfer roller 6
A transfer bias having a polarity opposite to that of the toner 53 (negative polarity in this embodiment) is applied to 0. Since the transfer roller 60 is in contact with the surface of the photoconductor drum 20, by increasing the resistance value thereof, the photoconductive layer 22 formed on the photoconductor drum 20 by the voltage applied to the transfer roller 60. The toner image on the photoconductor drum 20 is surely transferred onto the paper P so as to prevent the destruction of the paper.

On the other hand, on the photosensitive drum 20 after transfer,
The photoconductor drum 2 is not transferred to a portion corresponding to the printed portion.
0 there is residual toner left over. The residual toner is sequentially sucked and collected by the developing roller 56 of the developing unit 50, returned to the toner storage chamber 54, and used again for developing. The residual toner remains in the area corresponding to printing, but especially in the area corresponding to line drawing.
In many cases, a large amount of toner locally remains in the area corresponding to the black solid area. As described above, when a large amount of residual toner locally exists, it is difficult to suck and collect the toner by the developing roller 56. Therefore, in the present embodiment, a toner leveling brush for contacting and leveling the residual toner remaining on the photoconductor drum 20 is provided downstream of the transfer roller 60 in the rotational direction of the photoconductor drum 20. 42 is provided. In this way, by making the residual toner uniform, the recovery of the residual toner on the developing roller 56 is assisted. The behavior of the toner 53 between the developing roller 56 and the photosensitive drum 20 will be described in detail later.

The fixing unit 70 is provided on the downstream side of the photosensitive drum 20 in the conveying direction, and is composed of a heating roller 71 having a halogen lamp built therein and a pressing roller 72, and a toner image transferred to the lower surface of the paper P is formed. The paper P is fixed while being pressed while being heated.

On the downstream side of the fixing unit 70 in the transport direction, a pair of transport rollers 75 for transporting the paper and a paper discharge tray 77 are provided.

That is, as shown in FIG.
4, the paper feed roller 13 that forms a transport path PP that transports the paper P fed from 4, and the photoconductor drum 20.
The fixing unit 70 and the paper discharge tray 77 are arranged in a substantially linear shape.

Since the transport path PP has a substantially linear shape as described above, the laser printer of this embodiment can form an image regardless of the type of the paper P. For example, it is possible to easily print on thick and strong cardboard, envelopes, OHP sheets, and the like. However, since the transfer efficiency of these papers is lower than that of plain paper, the residual toner remaining on the photosensitive drum 20 after transfer tends to be larger than usual, and the suction and collection ability of the developing roller 56 is high. Otherwise, the above-mentioned ghost will occur. Therefore, in the apparatus having the substantially linear transport path PP as in the present embodiment, it is necessary to enhance the ability of the developing roller 56 to collect the residual toner.

Next, the first drive mechanism 80 for driving the photoconductor drum 20 and the sheet carrying system will be described with reference to FIG.

The first drive mechanism 80 is disposed on the outer surface side of the side wall portion on the left side facing the laser printer 1, and the rotational force of the gear 82 of the output shaft of the first drive motor 81 is the two-stage gear 83 ( 83a, 83b) and a two-stage gear 84 (84a, 84)
b) is transmitted to the gear 85, and the rotational force of the gear 85 is transmitted to the gear 13a that drives the sheet feeding roller 13 via the gear 86. Further, the rotational force of the gear 86 is applied to the gear 18 that drives the registration roller 18 via the gear 87.
a.

The rotational force of the two-stage gear 83 is the two-stage gear 89 (89a, 89b), the gear 90, and the two-stage gear 91 (9
1a, 91b) and the two-stage gear 92 (92a, 92b) to be transmitted to the gear 20a that drives the photosensitive drum 20.

On the other hand, the rotational force of the two-stage gear 92 is
And the gear 94 to the gear 71a for driving the heating roller 71. That is, when the first drive motor 81 is rotated in the clockwise direction, the paper feeding roller 13, the pair of registration rollers 17 and 18, the photoconductor drum 20, and the heating roller 71 rotate as indicated by the arrow. Since the sheet P is driven, the sheet P fed from the sheet feeding cassette 14 is conveyed along a predetermined conveying path PP and is ejected to the sheet ejection tray 77.

Next, the second drive mechanism 100 for driving the developing unit 50 will be described with reference to FIG.

This second drive mechanism 100 is arranged on the outer surface side of the side wall portion on the right side facing the laser printer 1, and the rotational force of the gear 102 of the output shaft of the second drive motor 101 is two steps higher than that of the gear 103. Gears 104 (104a, 104b) and 2
It is transmitted to the gear 52 a that drives the agitator 52 in the toner box 51 via the stepped gear 105 (105 a, 105 b) and the gear 106. Further, the rotational force of the gear 106 is transmitted via the gear 107 to the gear 56 a that drives the developing roller 56 and the gear 55 a that drives the supply roller 55.

That is, when the second drive motor 101 is rotated counterclockwise, the agitator 52 and the supply roller 5 are rotated.
5 and the developing roller 56 are rotationally driven as indicated by the arrow, so that the toner box 5 is rotated by the rotation of the agitator 52.
The toner 53 of No. 1 is supplied to the supply roller 55, and the toner of the toner 5 is supplied to the developing roller 56 by the rotation of the supply roller 55.
3 are supplied. Here, the photosensitive drum 20, the developing roller 56, and the supply roller 55 are driven in the same rotation direction, and the peripheral speed of the developing roller 56 is a predetermined peripheral speed that is at least twice the peripheral speed of the photosensitive drum 20. The drive speeds of the first drive motor 81 and the second drive motor 101 are set so that

Next, the operation and effect of the developing process by the reversal developing method will be described with reference to FIGS. 5 to 8 while explaining the set developing conditions.

In order to obtain "2.0" as the transmission density (image density) necessary for the image formed, as shown in FIG. 6, the toner adhesion amount to the paper, that is, the development toner amount is about 0. 78 mg / cm ² is required. On the other hand, in the case of solid black printing, if all the toner on the developing roller 56 is transferred to the photosensitive drum 20 (developing efficiency 100%), the developing area A is in front of the nip portion, and therefore there is no toner in the nip portion. Therefore, the developing roller 56 having a large friction coefficient and the photosensitive drum 20 are directly rubbed with each other, which causes a problem.

That is, in the present embodiment, the photosensitive drum 2
0 and the developing roller 56 rotate in the same direction,
In the part where the surfaces of both are in contact (nip part), both are relatively moving in opposite directions. At this time, if the developing efficiency becomes 100% and all the toner 53 on the developing roller 56 reaches the nip portion before it moves to the photosensitive drum 20 in the developing area A shown in FIG. 5,
In the nip portion, the developing roller 56 and the photosensitive drum 20
Makes direct contact with. Then, the coefficient of friction of the developing roller 56 is very large compared to the photoconductor drum 20, so that the rotation of the photoconductor drum 20 and the developing roller 56 becomes unstable, which causes deterioration of image quality.

Therefore, in the present embodiment, the developing roller 5
The total amount of toner conveyed to the developing area by (6) (conveyed toner amount) = (toner weight per unit area) × (peripheral speed of developing roller) is the amount of developing toner required to obtain a sufficient image density. The amount is set to be larger than 78 mg / cm ² with a certain allowance, and the toner 53 that acts as a lubricant for both is present in the nip portion between the photosensitive drum 20 and the developing roller 56.

FIG. 7 shows a graph of the developing characteristics in this embodiment.

The developing characteristic in the reversal developing is characterized in that the correlation between the effective developing bias (difference between the developing bias voltage and the electrostatic latent image voltage after exposure) and the developing toner amount becomes substantially linear. Then, when the developing efficiency reaches 100%, the developing characteristic reaches a peak, and thereafter, the amount of developing toner does not increase even if the effective developing bias increases.

On the other hand, as shown in FIG. 7, the inclination of the developing characteristic has a correlation with the toner charge amount. When the charge amount of the toner becomes high, the slope of the developing characteristic becomes small as shown by the chain line in FIG. 7, and the developing efficiency cannot reach 100% unless the effective developing bias is increased. On the contrary, when the charge amount of the toner becomes low, the slope of the developing characteristic becomes large as shown by the chain double-dashed line in FIG. 7, and the developing efficiency becomes 100% even if the effective developing bias is small.

By the way, in the present embodiment, when the developing efficiency reaches 100%, the above-mentioned problems occur. Therefore, it is necessary to increase the charge amount of the toner to some extent to reduce the inclination of the developing characteristic. Specifically, assuming that the amount of toner on the developing roller 56 is 0.5 mg / cm ² , the amount of charge of the toner is in the range of 20 to 25 μC / g (so that it falls within this range against environmental changes and changes in durability tests). Then, the first drive mechanism 80 and the second drive mechanism 100 described above are configured so that the peripheral speed of the developing roller 56 is 2.5 times the peripheral speed of the photosensitive drum 20. FIG. 7 is a graph showing the developing characteristics at this time. Then, for example, the developing roller 5
By setting the effective developing bias potential of No. 6 to 200 V, the image density is 2.0 or more while preventing the developing efficiency from becoming 100% even when the toner charge amount changes (20 to 25 μC / g). It is possible to maintain.
At this time, since the electrostatic latent image voltage after exposure on the photosensitive drum 20 is 100V, the developing bias voltage of the developing power source E actually applied to the developing roller 56 is set to 300V.

When the image forming process is started, first, the charge on the photoconductor drum 20 is wiped off by the static elimination lamp 41, and then the surface of the photoconductor drum 20 is charged by the charger 40 as shown in FIG. Is uniformly charged to about + 800V. Then, in this state, the laser light L emitted from the laser light emitter 31 according to the image data based on the image to be formed on the paper P is main-scanned by the polygon mirror 32, and the lenses 33 and 34 and the reflection mirror 35. , 36 onto the photosensitive drum 20 and the photosensitive drum 2
An electrostatic latent image is formed on 0. At this time, the voltage of the portion corresponding to the electrostatic latent image on the photosensitive drum 20 is attenuated and drops to about + 100V.

On the surface of the developing roller 56, with the developing bias voltage of about +300 V being applied, the toner 53 charged to the positive polarity is attached to the surface of the developing roller 56 with a layer thickness of more than one layer. Is not attracted to a charging voltage higher than its own voltage (about + 800V), and a lower electrostatic latent image voltage (about + 100V).
V), the toner 53 on the developing roller 56 is formed on the photoconductor drum 20 so that the difference between the electrostatic latent image voltage and the developing bias voltage (effective developing bias) is filled with the charge of the toner 53. It is attached only to the electrostatic latent image and developed.

This development is performed in the development area A, as shown in FIG. That is, the developing roller 56 and the photosensitive drum 2
Since 0 is relatively moving in the opposite direction in the nip portion, the toner 53 on the developing roller 56 is transferred to the photosensitive drum in the developing area A immediately before the contact between the developing roller 56 and the photosensitive drum 20. A transition is made to a portion corresponding to the electrostatic latent image on 20.

On the other hand, the residual toner remaining on the photosensitive drum 20 after the transfer also behaves according to the potential difference caused by the developing bias voltage, like the toner 53 on the developing roller 56. The residual toner is once charged to a charging voltage (+800 V) by the charger 40, and if the portion to which the residual toner is attached is irradiated with the laser beam L, the residual toner in that portion is usually as described above. Like the electrostatic latent image voltage, it drops to + 100V. Therefore, the toner 53 is newly attached to the portion to which the residual toner is attached by the developing roller 56, so that the disadvantage that the residual toner remains on the photosensitive drum 20 after the development does not occur.

However, since the residual toner adhered to the portion not irradiated with the laser beam is still charged to + 800V, when this residual toner approaches the vicinity of the nip portion with the developing roller 56, the charging voltage ( +8
00V) and the developing bias (+ 300V), the residual toner is transferred to the developing roller 56 and collected.

As for the process of simultaneously performing the development and the recovery on the developing roller 56, "Electrophotographic Society Journal, Vol. 30, No. 3, (1991) P. 29 (Hosoya et al.)" Is detailed. Please refer.

By the way, in addition to the force due to the developing bias, the residual toner also has a van der Waals force with the photoconductor drum 20, and therefore tends to remain on the photoconductor drum 20. In the present embodiment, since the photoconductor drum 20 and the developing roller 56 are relatively moved in the opposite directions at the closest position, there is an effect of scraping the residual toner by the developing roller 56, whereby the residual toner is removed. Since the toner is moved, the van der Waals force between the residual toner and the surface of the photoconductor drum 20 is canceled, the residual toner easily moves to the developing roller 56 by the developing bias, and the photoconductor drum after the developing process is completed. Two
No residual toner still remains in the unexposed areas above 0.

Further, when the developing roller 56 collects this residual toner, the photosensitive drum 20 and the developing roller 56 move relatively in opposite directions at the nip portion, and therefore, on the photosensitive drum 20. The residual toner is collected by the developing roller 56 by the action of the developing bias in the collecting area B immediately before reaching the nip portion. Therefore, since the residual toner does not enter the nip portion, the collecting area B does not overlap with the developing area A described above, and only the residual toner is collected in the collecting area B.

Here, as described above, the developing roller 56
And the surface of the photosensitive drum 20 move relatively in opposite directions at the closest position (nip portion), so that the electrostatic latent image is formed into a toner image by the developing roller 56 and the residual toner is developed by the developing roller 56. Since the suction and collection to and from 56 are separately performed before and after the nip portion, it is possible to enhance the suction and collection capability of the residual toner on the photosensitive drum 20. Further, since the developing roller 56 is formed of an elastic material having conductivity and the peripheral speed of the developing roller 56 is set to be twice or more the peripheral speed of the photoconductor drum 20, the residual toner is scratched by the developing roller 56. Due to the collecting effect, the ability to suck and collect the residual toner can be further enhanced.

By increasing the ability to collect residual toner as described above, in particular as in the above embodiment,
By providing the toner leveling brush 42 having a function of contacting with the residual toner and making it uniform, it is possible to prevent the occurrence of the above-mentioned ghost. Further, even when printing on special paper such as thick paper or envelope having low transfer efficiency in a low temperature and low humidity environment or a high temperature and high humidity environment, the residual toner remaining on the photoconductor drum 20 can be favorably collected by the developing roller 56. It is possible to prevent the occurrence of the ghost as described above.

Further, when the cleaning roller described in the section of the prior art is used instead of the toner leveling brush 42, even if crushed toner which is not suitable for the so-called cleanerless system is used as the toner 53, It is possible to prevent the above-mentioned ghost from occurring.

It should be noted that various modifications may be made to the above-described embodiment based on existing technology and technology obvious to those skilled in the art.

For example, the configurations of the first drive mechanism 80 and the second drive mechanism 100 are the types of toner 53 and the developing roller 56.
Elements such as the rotation speed of the developing roller 56, which are required according to the amount of toner adhered to the toner, are variable, or the first drive mechanism 80 and the second drive mechanism 100 are the same drive source. The developing roller 56 and the photoconductor drum 2 are driven by appropriately setting the gear ratio of the constituent gears.
You may make it provide the speed difference with 0.

Elastic rubber may be used as the layer thickness regulating blade 57 instead of metal. Further, instead of the charging device 40 of the scorotron system, a charging roller that contacts the photoconductor drum 20 may be used.

The transfer roller 60 may be replaced by a transfer brush or a non-contact corotron transfer device.

It is needless to say that the present invention can be applied not only to laser printers but also to image forming apparatuses of various electrophotographic systems such as copying machines and facsimiles.

[0079]

As is clear from the above description,
According to the image forming apparatus of the first aspect, the latent image is transferred to the toner by bringing the toner thin layer on the surface of the toner carrier of the developing unit into contact with the surface of the latent image holding member on which the latent image is formed by the latent image forming unit. Image. This toner image is transferred onto the image support surface by the image transfer means. On the other hand, the residual toner that has not been transferred and remains on the surface of the latent image holding member is sucked and collected in the developing means by the toner carrier. The surface of the latent image carrier is driven in a predetermined direction in synchronization with the conveyance of the image carrier by the first driving means. The surface of the toner carrier is driven in a direction relatively opposite to the moving direction of the latent image carrier surface at the position closest to the surface of the toner carrier by the second driving means. The latent image carrier surface and the toner carrier surface are driven in relatively opposite directions at the closest position, so that the latent image is formed into a toner image by the upstream side in the moving direction of the toner carrier surface from the closest position of both. The residual toner is sucked and collected on the downstream side in the moving direction of the surface of the toner carrier from the closest position of both, so that the toner image formation and the suction and collection are performed separately. It is possible to improve the ability.

According to the image forming apparatus of the second aspect, the same effect as that of the first aspect can be obtained, and by using the conductive elastic roller for the toner carrier, the friction of the surface of the toner carrier can be achieved. It is possible to increase the coefficient, and as a result, the toner conveying force becomes stronger, so that it becomes possible to further improve the suction and collection ability of the residual toner.

According to the image forming apparatus of the third aspect, the same effect as that of the first or second aspect is obtained, and the moving speed of the surface of the toner carrying member is twice as fast as the moving speed of the surface of the latent image holding member. By the above, the scraping effect of the residual toner on the surface of the toner carrier is increased, and the suction of the residual toner,
It is possible to further increase the recovery capacity.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view of a laser printer according to an embodiment of the present invention.

FIG. 2 is an enlarged side view of a developing unit.

FIG. 3 is a configuration diagram of a gear system of a first drive mechanism.

FIG. 4 is a configuration diagram of a gear system of a second drive mechanism.

5 is an enlarged side view of a main part of FIG.

FIG. 6 is a diagram relating to transmission density and developing toner amount.

FIG. 7 is a diagram relating to a developing toner amount and an effective bias voltage.

FIG. 8 is an explanatory diagram illustrating a developing process by a reversal developing method.

FIG. 9 is a configuration diagram of a so-called cleanerless type laser printer according to a conventional technique.

[Explanation of symbols]

 1 Laser Printer 10 Feeder Unit 13 Paper Feed Roller 20 Photosensitive Drum 30 Laser Scanner Unit 50 Developing Unit 53 Toner 55 Supply Roller 56 Developing Roller 60 Transfer Roller 70 Fixing Unit 77 Paper Discharging Tray 80 First Driving Mechanism 81 First Driving Motor 100 Second drive mechanism 101 Second drive motor P Paper PP Transport path

Claims (3)

[Claims] 1. A latent image forming means for forming a latent image on the surface of a latent image holding member and a toner thin layer formed on the surface of a toner carrying member are brought into contact with the surface of the latent image holding member on which the latent image is formed. The image forming apparatus includes a developing unit for converting the toner image into a toner image, and an image transferring unit for transferring the toner image onto the surface of the image support, and the developing unit converts the latent image into a toner image, and after the transfer, on the latent image holding member surface. An image forming apparatus for collecting the residual toner remaining on the toner carrier by the toner carrier, a first driving unit that drives the latent image carrier in a predetermined direction in synchronization with the conveyance of the image carrier, and the toner carrier. An image forming apparatus comprising: a second drive unit that drives a surface in a position closest to the surface of the latent image carrier in a direction relatively opposite to a moving direction of the surface of the latent image carrier. 2. The image forming apparatus according to claim 1, wherein the toner carrier is an elastic roller having conductivity. 3. The moving speed of the surface of the toner carrier by the second driving means is set to be twice or more the moving speed of the surface of the latent image holding body by the first driving means. The image forming apparatus according to claim 1 or 2.